Most Habitable Planets Will Be Waterworlds, New Study Suggests

A new study has concluded that in the search for habitable planets, most found to be suitable for life will likely be watery worlds with very little or no dry land. In fact, most habitable planets will have less than 10 percent land mass.

By constructing a statistical model to predict the quantitative division between land and water on habitable exoplanets, it was determined, Phys.org reports, that most habitable planets would have oceans covering over 90 percent of their surfaces. Built by Dr. Fergus Simpson of the Institute of Cosmos Sciences at the University of Barcelona, the conclusion derived from the predictive model followed Earth’s own example — a rocky world with over 70 percent of its surface area covered by water. Earth itself is very close to being what scientists refer to as a “waterworld.”

In the movie Waterworld, star Kevin Costner is a lone wolf sailor on a planet covered with water, appropriately enough given the title. The planet is Earth, of course, in a future where all the ice caps have melted, leaving the world awash and regressive, a Mad Max spin that replaces barren wastes for — with a nod to Samuel Coleridge — water, water everywhere. Waterworld is a cautionary tale that pushes the idea of global warming to its extreme results.

Unlike Waterworld (Earth), though, most habitable worlds will not become endless singular oceans as a result of the denizens of a particular world. No, the exoplanets will already be waterworlds.

Dr. Simpson explained.

“A scenario in which the Earth holds less water than most other habitable planets would be consistent with results from simulations, and could help explain why some planets have been found to be a bit less dense than we expected.”

Simpson found that for a planetary surface to entertain both land and water in abundance, a fragile balance between the volume of water the world returns over a period of time and how much space is needed for storage in the world’s oceanic depths. The study showed that both quantities can vary a great deal across the graduated arc (from worlds with over 90 percent water coverage to worlds without land mass at all) of waterworlds. As for the Earth itself and its surface coverage of 70 percent water, just why the balance exists has been and continues to be, as Phys.org describes it, “an unresolved and long-standing conundrum.”

Simpson has suggested, using the results of the study, that the balance reached on Earth may actually be a consequence of the anthropic principle — the idea that human observations of the Universe are influenced by requirements for the formation of sentient alien life. It is the leading principle behind the estimation of habitable zones (or “Goldilocks zones,” the area a particular star where a planet is able to generate and retain liquid water), where the assumption is that liquid water is necessary for the development and sustainability of living organisms.

Earth is almost a waterworld, its surface covered by more than 70 percent with water. [Image by Triff/Shutterstock]

“Based on the Earth’s ocean coverage of 71%,” Simpson noted in his study, which was published in the most recent Monthly Notices of the Royal Astronomical Society, “we find substantial evidence supporting the hypothesis that anthropic selection effects are at work.”

So what does this mean for astronomers and astrobiologists in search of alien life? It means that, with regard to exoplanets that might be home to living organisms that have evolved from similar chemical systems as life on Earth, the search for habitable planets will likely find that most of the candidates will be waterworlds with limited areas of dry land, if there is any at all.

Artist's concept of an exoplanet covered in water, a waterworld. [Image by GiroScience/Shutterstock]

Simpson also noted that simply being a habitable planet does not necessarily mean that life will evolve there.

“Our understanding of the development of life may be far from complete,” he said, “but it is not so dire that we must adhere to the conventional approximation that all habitable planets have an equal chance of hosting intelligent life.”

Besides Simpson’s statistical model work, it also has been found, according to a study on exoplanets that might form in orbit in binary star systems, that it is not only possible for waterworlds to exist with two suns (as opposed to the popular idea that two-sun exoplanets would be desert worlds like Tatooine in the film Star Wars), but that, given the right conditions, they would be habitable planets as well.